1. Field of the Invention
This invention relates generally to the art of pumps and more particularly to a peristaltic pump.
2. Description of the Prior Art
Peristaltic pumps, of the type to which the present invention is directed, have wide and varied applications. For example, the pump may be used for dispensing drugs or the like. In such an application it is necessary that the pump have a wide range of adjustment in order to vary the rate of flow which must be accurately determined and calibrated. The pump must be free of internal valves and other parts which create a problem of cleaning and sterilization. The pump must be capable of being put into operation quickly and easily without complicated connections and adjustments. For reliability in operation the pump must be of simple construction with a minimum number of working parts. Pumps of this type may be used for controlling the flow and composition of a fluid mixture in operation that requires delivery of a fluid having a flow that is constantly metered and whose composition is regulated within very narrow tolerances. It is also necessary in some of these applications to continuously or periodically change the composition of the fluid. Thus, with continuous change in composition, it is possible to provide a fluid stream, the composition of which can be made to vary over an entire spectrum of compositions. Industrial applications for such a device include those instances where fluid reactant compositions must be metered and their composition must be programmed over a given period.
One of the well-known types of peristaltic pumps utilizes cyclic deformation of a flexible wall tube by means of rotary cams. However, with these prior art pumps it is not usually possible to vary the output thereof over a wide range unless the speed of rotation of the cams is changed and this is difficult, particularly where AC motors are used for driving the cams. One means for overcoming this particular prior art problem is disclosed in U.S. Pat. No. 3,658,445 granted to Pulman et al. The pump of the Pulman et al patent includes a reciprocating element which alternately pinches and releases a flexible wall tube. On either side of the pumping element, reciprocating inlet and outlet closure elements are provided. When the pumping element pinches a tube during a pumping stroke the inlet closure element closes the tube while the outlet closure element releases the tube. During induction strokes, as the pumping element releases the tube, the inlet closure element is opened while the outlet element is closed. Synchronized operation of the pumping element, as well as the inlet and outlet elements, is achieved by associated cams. However, it should be noted that the movement of the associated cams is perpendicular to that of the linear actuator.
However, in contrast to the present invention which will be described fully hereinafter, the Pulman et al. disclosure does not teach the opening and closing of the inlet and outlet closure elements in timed relationship with each other as well as in timed relationship with the pumping element. In the Pulman et al. patent, the pump is provided with means for varying the stroke of the pumping element so as to vary the pump output. This, too, is in contrast to the structure and method of operation of the present invention. The present invention is further distinguished over the Pulman et al. structure in that, as will be described hereinafter, a single, primary, two-part cam is used for both the inlet and outlet elements while a secondary cam, responsive to the movement of the primary cam is used for the pumping element.
U.S. Pat. No. 3,359,910 granted to Lapham, Jr. discloses another form of peristaltic pump. In the Lapham, Jr. patent, the peristaltic-like fluid pump utilizes a flexible tube in combination with inlet and outlet valves which are under the control of the rotation of a cam. Cam driven actuating means associated with the inlet and outlet valves are adapted to alternately actuate force applying means such that external force is applied when the outlet valve means is open. The external force is released when the inlet valve is open. The cam driven actuating means associated with the valve means is mechanically connected to the actuating means through reduction gears so that the cam driven actuating means may operate at a predetermined speed. As will be explained more fully hereinafter, the present invention provides different structure for regulating the flow of fluid.
U.S. Pat. No. 3,007,416 granted to Childs is related to fluid pumps of the type that are capable of simulating the action of a human heart in pumping blood through the human system. The Childs' pump utilizes a flexible element of readily deformable material having a passage for passing fluid. The flexible element is positioned in a housing such that it extends through and divides the housing into separate chambers. One end of the flexible element is adapted to be connected to a suitable source of fluid and the other end is connected to a receiver for the fluid. The chambers are adapted to be connected to a source providing positive and negative pressures such that the pressures are applied to portions of the element in predetermined sequence to produce flow of the fluid through the element. However, there is no suggestion in the Childs' patent for the timed actuation of separate inlet plunger means, outlet plunger means and extruder plunger means such as contemplated by the present invention and as will be described more fully hereinafter.
Still another form of prior art pump is disclosed in U.S. Pat. No. 2,412,397 granted to Harper, in which there is disclosed a pump comprising a flexible walled pump chamber with which is associated a flexible walled inlet valve and a flexible walled outlet valve. Means are also provided for compressing or squeezing the walls of the valves and the pump chamber in order to obtain a movement of fluid from an inlet connection to a discharge connection. The Harper patent provides means for squeezing or compressing the tubular member to seal off portions thereof in order to provide inlet and outlet valve means and for varying the capacity of a portion thereof in order to produce a pumping action by a movement transversely of a length of the tubular member without any longitudinal component to such movement. The structure in the Harper patent is intended to overcome the problem of stretching of the tubular member during the squeezing thereof. More specifically, Harper discloses a flexible tubular member and first reciprocating means for sealing off a portion of the tubular member from the inlet conduit thereof. Second reciprocating means are spaced from the first reciprocating means for sealing off a portion of the tubular member from the discharge conduit. Third reciprocating means engage the tubular member to alternately decrease and increase the capacity thereof between the sealing means. Harper does not suggest that the third reciprocating means is responsive, in timed relationship, to the movement of the first and second reciprocating means as is taught by the present invention which will be described more fully hereinafter.
Still another U.S. Pat. No. 3,778,195 granted to Bamberg discloses a pump that includes a shaft driven by a motor and a plurality of cams spaced along the shaft with the cams being angularly and sequentially offset from one another. The cams interact with spring loaded members which, in turn, sequentially squeeze shut a flexible, disposable tubing held in place by support means. Bamberg controls the rate of flow of the fluid through the tubing by an adjusting mechanism which engages the spring loaded members that sequentially compress the tubing and thereby controls the cross sectional flow area of the tubing. Bamberg does not suggest that one cam is responsive to the movement of another cam, as is taught by the present invention.
Still another application of a pump of the type to which the present invention is directed is a heart pump used to pump blood to bypass the blood around a living heart. For example, such heart pumps must be operable without producing turbulence and stagnation of the blood and in addition, at slow pumping rates, cannot produce back flow or regurgitation of the blood resulting in low efficiency fluid transfer. Moreover, at rapid pumping rates, damage to the blood by hemolysis due to rapid and excessive forces applied in the pumping and valving operations must be prevented. In a heart pump it is necessary that violent spurts of the blood are not permitted since this can also result in damage to the blood. Where a chemical mixture or composition of the blood must be determined, it is frequently desirable that the quantity of fluid withdrawn be within closely defined limits and that the apparatus employed permit withdrawal in small precise quantities as well as in larger amounts. For example, drop-by-drop extraction under complete control of the operator is very frequently a matter of considerable importance in some medical, scientific and manufacturing operations. When used as an extracorporeal heart, the pump must be capable of immediate adjustment upon any change in the flow characteristics of the vascular system. When used as an artificial heart, the pump will affect the vascular flow and a complex, virtually uncontrollable feed-back relation exists between the artificial heart and the vascular system of the subject. For example, during open heart surgery, a technician is continually instructed by the surgeon as to the starting, stopping and adjustment of the pump operations. A difficult, coordinated effort is required. Continuous monitoring is necessary. It is therefore essential that the pump be capable of delivering a wide range of quantities for long periods of time.